The present invention relates to a method for producing poly(p-t-butoxystyrene).
More specifically, the present invention relates to a method for producing poly(p-t-butoxystyrene) by a polymerization of p-t-butoxystyrene characterized in that the raw material, the p-t-butoxystyrene or a solution thereof, has a water content in a specific range and is added to a mixture of a reaction solvent and a polymerization initiator.
Poly(p-t-butoxystyrene) is well-known as a raw material of resist used for producing LSI and the like. In recent years, those having narrow molecular weight distribution, particularly those having "weight average molecular weight(Mw) /number average molecular weight(Mn)" about 1.30 or smaller, more preferably 1.20 or smaller, are desired.
As an example of method for producing poly(p-t-butoxystyrene), JP-A-6-298869 discloses a method in which a solution of p-t-butoxystyrene is added to a mixture of a reaction solvent and a polymerization initiator.
According to this method, however, poly(p-t-butoxystyrene) having narrow molecular weight distribution is not necessarily obtained, and the compound having Mw/Mn exceeding 1.30 is often produced. Therefore, this method has an industrial problem.
On the other hand, as a method for obtaining poly(p-t-butoxystyrene) having narrow molecular weight distribution securely, a method in which a polymerization initiator is added at a stroke to a mixture of a reaction solvent and p-t-butoxystyrene is known(JP-A-8-29983). Although poly(p-t-butoxystyrene) having narrow molecular weight distribution can be obtained according to this method, the addition of polymerization initiator in a very short period causes very rapid proceeding of the exothermic reaction and abrupt heat generation. As a result, the temperature control becomes difficult, and this method also has an industrial problem.
The present inventors have conducted extensive studies to resolve the above problems of the conventional methods, and to develop a method for producing poly(p-t-butoxystyrene) having narrow molecular weight distribution securely not causing abrupt heat generation.
As a result, they have found that, when poly(p-t-butoxystyrene) is produced by a method in which p-t-butoxystyrene or a solution thereof is added to a mixture of a reaction solvent and a polymerization initiator, the molecular weight distribution of poly(p-t-butoxystyrene) is affected by water contained in the raw material, p-t-butoxystyrene or a solution thereof, as an impurity, and that poly(p-t-butoxystyrene) having narrow molecular weight distribution can be produced securely by using a p-t-butoxystyrene having water content in a specific range of 5-70 ppm. Thus, the present invention has been completed.